On an isolated island surrounded by endless blue sea, a man code-named "Zero" woke up from a coma and lost all his memory. The only companion on the island is the guarded mysterious woman "No. 7". This seemingly paradise island is full of weirdness: food appears at regular intervals, black obelisk that triggers memory fragments, and the weather never changes. As the investigation deepened, Zero was horrified to discover that this place was not a prison, but a high-tech memory sanatorium called "Forgotten River", and he himself was the creator of this island of memory. When the price of forgetting comes to light, he must retrieve the truth from his broken memories and face the guilt he buried with his own hands.
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